With the epidemic of obesity and the population's aging the prevalence of type 2 diabetes mellitus is increasing. Insulin resistance is a hallmark of type 2 diabetes. This application's long-term objectives are to understand how insulin's signals are communicated within cells and how this process is defective in insulin resistant states. The adipocyte plays a central role in insulin resistance, and skeletal muscle is the major site of glucose disposal after a meal. Preliminary results in adipocytes lead to the hypothesis that the membrane protein flotillin-1 recruits specific signaling molecules to a compartment of the plasma membrane and that this recruitment is required for the increase in cell surface glucose transporters that occurs in response to insulin. These events constitute a second signaling pathway required for insulin-stimulated glucose transport that is independent of phosphatidylinositol 3-kinase. Specific Aim 1 is to define the function of flotillin-1 in glucose metabolism by manipulating its expression in cultured adipocytes and muscle cells. Relationships between flotillin-1 expression level and indices of glucose metabolism and insulin action will be determined. Specific Aim 2 is to define the function of flotillin-1 in glucose metabolism with genetically engineered mice. Mice that overexpress flotillin-1 in adipose tissue and in skeletal muscle and mice that express no functional flotillin-1 will be generated and their phenotypes carefully analyzed with respect to glucose and lipid metabolism. These genetically engineered mice will be valuable reagents to study the physiology of whole body glucose homeostasis. Specific Aim 3 is to investigate the regulation of flotillin-1 by identifying the proteins that interact with it in the yeast two-hybrid system. Completion of these aims should yield testable hypotheses about the role of flotillin-1 in human health and disease and in the pathophysiology of type 2 diabetes.